1. Field of the Invention
The present invention relates to control systems for plunger-type fuel pumps of internal combustion engines.
2. Description of the Related Art
Conventionally, plunger-type fuel pumps are known that take up fuel from a fuel tank of an internal combustion engine and pump the pressurized fuel to an injector or a carburetor (see for example Japanese Patent Kokai (Laid-open publication) No. 08-114179). A typical plunger-type fuel pump includes a cylindrical plunger, a spring, a coil and an oscillation circuit. The cylindrical plunger has a piston made of a magnetic material. The piston is urged in the fuel-ejecting direction by the spring. When the coil is excited, the coil moves the piston in the direction (fuel-take-in direction) to take the fuel into the plunger. The oscillation circuit intermittently energizes the coil. When a power source voltage is supplied to the oscillation circuit, the plunger piston shifts alternately in the fuel-take-in direction and the fuel-ejecting direction, due to the intermittent energizing of the coil by the oscillation circuit and the biasing force of the spring. This reciprocating movement of the plunger piston leads to a pump operation to eject the fuel.
Some electronic fuel injection systems of internal combustion engines use such a plunger-type fuel pump. When an ignition switch is turned on, the fuel pump is driven periodically at a predetermined frequency. However, pressure variations occur in the fuel pumped to the injector due to the reciprocating motion of the plunger piston. Thus, there is a problem that even if the time for which the valve of the injector is open is held constant, the fuel injection amount varies due to the pressure variations of the fuel, so that the combustion state may become unstable.
It is thus an object of the present invention to provide a control system for a plunger-type fuel pump that makes a stable combustion possible even when there are pressure variations in the fuel that is pumped to the injector.
In accordance with one aspect of the present invention, there is provided an improved control system for a plunger-type fuel pump in an internal combustion engine. The plunger-type fuel pump pumps fuel to an injector from a fuel tank such that the injector can inject the fuel into a cylinder. The control system includes means for detecting an injection start timing of the injector, and means for driving the fuel pump for a second predetermined time that starts a first predetermined time earlier than the injection start timing.
With this control system, it is possible to achieve a stable combustion, even when there are pressure variations in the fuel that is pumped to the injector.
Other objects, aspects and advantages of the present invention will become apparent to those skilled in the art when the following detailed description and the appended claims are read and understood in conjunction with the accompanying drawings.